Siloxane resin compositions

ABSTRACT

Addition curable silicone resin compositions have excellent processing characteristics, and can be used to encapsulate electrical and electronic devices.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Phase of PCT Appln. No.PCT/EP2016/080087 filed Dec. 7, 2016, which claims priority to GermanApplication No. 10 2015 225 921.8 filed Dec. 18, 2015, the disclosuresof which are incorporated in their entirety by reference herein.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention relates to siloxane resin compositions, to processes forproduction thereof and also to the use thereof in the manufacture ofelectrically isolating shaped articles and optical semiconductorelements.

2. Description of the Related Art

Binders and preparations to be used in the manufacture of electricallyisolating component parts have to meet extensive and demandingrequirements, including for example:

-   -   good surface hardness;    -   coupled with flexibility;    -   good lightfastness;    -   good weathering resistance;    -   good thermal stability;    -   low gas transmission and thus avoidance of corrosion;    -   high transparency;    -   high refractive index;    -   no yellowing (discoloration due to heat);    -   good technical properties in processing, for example good        shaping properties, rapid and controllable cure to the shaped        article, robust, error-tolerant processing properties,        process-adapted viscosity; and    -   cost efficiency;        although not all these properties have to be equally highly        developed in every application.

There have already been many prior art proposals. WO-A 15014890 and U.S.Pat. No. 7,527,871 may be referenced by way of example.

The use of addition-crosslinking silicone compositions for theproduction of LEDs is already known. They are oftentimes multicomponentsystems consisting of at least one organopolysiloxane having at leasttwo aliphatically unsaturated groups in the molecule and at least oneorganohydropolysiloxane having two or more Si—H groups in the moleculeand also at least one hydrosilylation catalyst and usually furtherformulation components. In the majority of preparations, the twocomplementary Si—H and Si-vinyl functions required for thehydrosilylation reaction are shared between various polyorganosiloxanesin the preparation.

SUMMARY OF THE INVENTION

The invention provides compositions containing

(A) organopolysiloxanes formed of at least 3 units of the formula

R¹ _(a)R² _(b)R³ _(c)H_(d)(RO)_(e)SiO_((4-a-b-c-d-e)/2)  (I),

where

-   R¹ represents monovalent, SiC-bonded, optionally halogen- or    cyano-substituted, hydrocarbyl moieties with aliphatic carbon-carbon    multiple bonding and may be the same or different at each    occurrence,-   R² represents monovalent, SiC-bonded, optionally halogen- or    cyano-substituted, saturated hydrocarbyl moieties and may be the    same or different at each occurrence,-   R³ represents identical or different monovalent SiC-bonded aromatic    moieties,-   R represents a hydrogen atom or monovalent, optionally substituted    hydrocarbyl moieties, which may be interrupted by heteroatoms, and    may be the same or different at each occurrence,-   a is 0, 1, 2 or 3, preferably 0 or 1,-   b is 0, 1, 2 or 3, preferably 0 or 2,-   c is 0, 1, 2 or 3, preferably 0 or 1,-   d is 0, 1 or 2, preferably 0 or 1, and-   e is 0, 1 or 2, preferably 0 or 1, in particular 0,    with the proviso that the a+b+c+d+e sum is not more than 3, the sum    total of Si-bonded hydrogen atoms and R¹ moieties per molecule is at    least 3, the a+b+c+d sum is equal to 0 or 1 in at least 10 mol % of    the units of formula (I), and c is other than 0 in at least one    unit,    optionally (B) organopolysiloxanes formed of units of the formula

R⁴ _(f)R⁵ _(g)R⁶ _(h)(R⁷O)_(i)SiO_((4-f-g-h-i)/2)  (VI)

where

-   R⁴ represents monovalent, SiC-bonded, optionally halogen- or    cyano-substituted, hydrocarbyl moieties with aliphatic carbon-carbon    multiple bonding and may be the same or different at each    occurrence,-   R⁵ represents monovalent, SiC-bonded, optionally halogen- or    cyano-substituted, saturated hydrocarbyl moieties and may be the    same or different at each occurrence,-   R⁶ represents identical or different monovalent SiC-bonded aromatic    moieties,-   R⁷ represents a hydrogen atom or monovalent, optionally substituted    hydrocarbyl moieties, which may be interrupted by heteroatoms, and    may be the same or different at each occurrence,-   f is 0, 1, 2 or 3, preferably 0 or 1,-   g is 0, 1, 2 or 3, preferably 1 or 2,-   h is 0, 1 or 2, preferably 0 or 1, and-   i is 0 or 1, preferably 0,    with the proviso that the f+g+h+i sum is not more than 3,    siloxanes (B) have at least two R⁴ moieties per molecule, the    f+g+h+i sum is equal to 0 or 1 in not more than 20 mol % of the    units of formula (VI) and h is other than 0 in at least one unit of    formula (VI),    (C) organopolysiloxanes formed of units of the formula

R⁸ _(k)R⁹ _(l)R¹⁰ _(m)(R¹¹O)_(n)SiO_((4-k-l-m-n)/2)  (X),

where

-   R⁸ represents monovalent, SiC-bonded, optionally halogen- or    cyano-substituted, hydrocarbyl moieties with aliphatic carbon-carbon    multiple bonding and may be the same or different at each    occurrence,-   R⁹ represents monovalent, SiC-bonded, optionally halogen- or    cyano-substituted, saturated hydrocarbyl moieties and may be the    same or different at each occurrence,-   R¹⁰ represents identical or different monovalent SiC-bonded aromatic    moieties,-   R¹¹ represents a hydrogen atom or monovalent, optionally substituted    hydrocarbyl moieties, which may be interrupted by heteroatoms, and    may be the same or different at each occurrence,-   k is 0, 1, 2 or 3, preferably 0 or 1,-   l is 0, 1, 2 or 3, preferably 0, 1 or 2,-   m is 0, 1 or 2, preferably 0 or 1, and-   n is 0 or 1, preferably 0,    with the proviso that the k+l+m+n sum is not more than 3,    siloxanes (C) have at least two R⁸ moieties per molecule, the    k+l+m+n sum is equal to 0 or 1 in at least 10 mol % of the units of    formula (X) and m is other than 0 in at least one unit of formula    (X),    and also    optionally (D) a catalyst to promote the addition of Si-bonded    hydrogen onto aliphatic carbon-carbon multiple bonds.

Preferably, in the siloxanes (A), not only Si-bonded hydrogen atoms butalso R¹ moieties are overwhelmingly, preferably exclusively, bonded tosilicon atoms of units of formula (I) where the a+b+c+d+e sum equals 3.More preferably, in the siloxanes (A), not only Si-bonded hydrogen atomsbut also R¹ moieties are overwhelmingly, preferably exclusively, bondedto silicon atoms of units of formula (I) where the a+b+c+d sum equals 3,i.e. to so-called M units, bearing no (OR) groups. These terminalfunctionalities in siloxane (A) ensure their ready accessibility andavailability for chemical reactions with a complementarilyfunctionalized reactant entity. This yields the surprising advantagethat merely a minimum of functional groups is needed in order to arriveat a solid cured body.

The (A) siloxanes employed according to the invention contain units offormula (I) where a+b+c+d is 0 or 1 in amounts of preferably at least 20mol %, more preferably at least 25 mol %, yet more preferably at least30 mol %, and most preferably 35 to 70 mol %. Since units of formula (I)where a+b+c+d is 0 can, depending on the profile of requirements, easilylead to some usually undesired embrittlement, units of formula (I) wherea+b+c+d is 1 are preferable as branching units.

The (A) siloxanes employed according to the invention preferably do notcontain any units of formula (I) where a+b+c+d=0.

Units of formula (I) where a+b+c+d is 2 may be used inter alia toestablish the mechanical properties, since they plasticize andflexibilize. The (A) siloxanes employed according to the inventionpreferably contain not more than 25 mol % of units of formula (I) wherea+b+c+d=2, preferably not more than 5 mol %, more preferably not morethan 2 mol %, most preferably none.

Preferably, the R¹, R⁴ and R⁸ moieties each comprise, independently ofeach other, hydrocarbyl moieties having aliphatic multiple bonding andfrom 2 to 8 carbon atoms, such as vinyl, allyl, methallyl, 2-propenyl,3-butenyl, 4-pentenyl, 5-hexenyl, 1,3-butadienyl, hexadienyl,cyclopentenyl, cyclopentadienyl, cyclohexenyl, ethynyl, propargyl,2-propynyl and isoprenyl, of which vinyl and allyl are particularlypreferable, most preferably vinyl.

Examples of R², R⁵ and R⁹ moieties are, independently of each other,alkyl moieties such as methyl, ethyl, n-propyl, isopropyl, n-butyl,isobutyl, tert-butyl, n-pentyl, isopentyl, neopentyl, and tert-pentyl,hexyl such as n-hexyl, heptyl such as n-heptyl, octyl such as n-octyland isooctyl such as 2,2,4-trimethylpentyl, nonyl such as n-nonyl, decylsuch as n-decyl, dodecyl such as n-dodecyl, and octadecyl such asn-octadecyl, and cycloalkyl such as cyclopentyl, cyclohexyl, cycloheptylor methylcyclohexyl.

Preferably, the R², R⁵ and R⁹ moieties independently of each othercomprise saturated hydrocarbyl moieties having from 1 to 12 carbonatoms, more preferably saturated hydrocarbyl moieties having from 1 to 4carbon atoms, most preferably methyl.

Examples of R³, R⁶ and R¹⁰ moieties are, independently of each other,aryl such as phenyl, naphthyl, anthryl or phenanthryl, indenyl,benzophenyl, fluorenyl, xanthenyl and anthronyl; aryloxyaryl moietiessuch as o-phenoxyphenyl and p-phenoxyphenyl; alkaryl moieties such aso-, m-, p-tolyl moieties, xylyl moieties and ethylphenyl moieties; andaralkyl moieties such as benzyl, α-phenylethyl and β-phenylethyl.

Preferably, the R³, R⁶ and R¹⁰ moieties comprise, independently of each,other aryl moieties such as phenyl or naphthyl, more preferably phenyl.

Examples of R, R⁷ and R¹¹ moieties are the moieties indicated for R² andR³.

More preferably, the R, R⁷ and R¹¹ moieties are hydrogen, methyl orethyl, yet more preferably hydrogen.

Component (A) preferably comprises siloxanes having at least 3 unitsselected from those of the formulae

R¹ _(a)R² _(b)R³ _(c)H_(d)(RO)_(e)SiO_(1/2) where (a+b+c+d+e)=3  (II),

R² _(b)R³ _(c)(RO)SiO_(2/2) where (b+c)=1  (IIIa),

R² _(b)R³ _(c)SiO_(2/2) where (b+c)=2  (IIIb),

R² _(b)R³ _(c)(RO)_(e)SiO_(3/2) where (b+c+e)=1  (IV), and

SiO_(4/2)  (V),

where R, R¹, R², R³, a, b, c, d and e are each as defined above, withthe proviso that not more than 25 mol %, more preferably not more than 5mol %, of the units in siloxanes (A) conform to formula (IIIb), the sumtotal of Si-bonded hydrogen atoms and R¹ moieties per molecule is atleast 3, at least one R³ moiety is present per molecule and at least oneunit of formula (IV) and/or (V) is present.

The (A) siloxanes preferably consist of 3 to 1000, more preferably 3 to150, and most preferably 3 to 50 units of formula (I).

The (A) siloxanes preferably contain at least 5 mol % of units offormula (II), at least 30 mol % of units of formula (IV), at most 25 mol% of units of formula (IIIb) and at most 20 mol % of units of formula(V).

More preferably, component (A) comprises siloxanes consisting of atleast one unit selected from R² ₃SiO_(1/2), R¹R² ₂SiO_(1/2), R²₂HSiO_(1/2), R² ₂R³SiO_(1/2), R²R³ ₂SiO_(1/2), R¹R²R³SiO_(1/2) andR²R³HSiO_(1/2) units and also at least one unit selected fromR³SiO_(3/2), ROSiO_(3/2) and R²SiO_(3/2) units and also optionally units(IIIb) selected from R² ₂SiO_(2/2), R²R³SiO_(2/2) and R³ ₂SiO_(2/2)units and also optionally R² (RO) SiO_(2/2) and R³ (RO) SiO_(2/2) units,where R, R¹, R² and R³ are each as defined above,

with the proviso that the siloxanes (A) have at least 3 siloxy units,the sum total of Si-bonded hydrogen atoms and R¹ moieties per moleculeis at least 3 and at least one R³ moiety is present per molecule and atmost 25 mol % of units of formula (IIIb) are present.

Preferred examples of component (A) are siloxanes consisting of at leastone unit selected from Me₃SiO_(1/2), ViMe₂SiO_(1/2), Me₂HSiO_(1/2),Me₂PhSiO_(1/2), MePh₂SiO_(1/2), ViMePhSiO_(1/2) and MePhHSiO_(1/2) unitsand also at least one unit selected from PhSiO_(3/2), HOSiO_(3/2),Ph(HO)SiO_(2/2), and MeSiO_(3/2) units where Me is methyl, Vi is vinyland Ph is phenyl,

with the proviso that the siloxanes (A) consist of 3 to 50 siloxy units,the sum total of Si-bonded hydrogen atoms and vinyl moieties permolecule is at least 3 and at least one phenyl moiety is present permolecule.

The (A) siloxanes used according to the invention preferably have no(OR) moieties. When, however, they do have (OR) moieties, for example asa consequence of the method of synthesis, the amounts are preferably ≤5wt %, more preferably ≤5000 weight ppm, most preferably ≤1000 weightppm.

The molar fraction of Si-bonded hydrogen atoms as a proportion of thetotal number of Si-bonded moieties in siloxane (A) is preferably from0.1 to 50%, more preferably from 2 to 40%, most preferably from 5 to30%. Determination is preferably by ²⁹Si NMR spectroscopy.

The molar fraction of R¹ moieties as a proportion of the total number ofSi-bonded moieties in siloxane (A) is preferably from 1 to 50%, morepreferably from 1 to 40%, and most preferably from 5 to 30%.Determination is preferably by ²⁹Si NMR spectroscopy.

The ratio of Si-bonded hydrogen atoms to Si-bonded R¹ moieties in the(A) siloxane employed according to the invention is preferably from 0.1to 9, more preferably from 0.8 to 7, yet more preferably from 0.9 to 5,and most preferably from 1.0 to 2.5.

The molar fraction of silicon atoms bearing at least one aromatic moietyR³ as a proportion of the total number of silicon atoms in siloxane (A)is preferably at least 30%, more preferably from 40% to 75%, and mostpreferably from 45% to 60%.

Siloxanes (A) preferably have an average molecular weight Mw ofpreferably at least 600 g/mol, more preferably at least 700 g/mol, yetmore preferably at least 800 g/mol, and most preferably between 900 and5000 g/mol, while the polydispersity is preferably at most 20, morepreferably at most 15, yet more preferably at most 10, and mostpreferably at most 6, measured using SEC with THF as the mobile phase, aconcentration of 5 mg/ml, and using an RI detector, against polystyreneas a standard.

The (A) siloxane resins employed according to the invention may eithersolid or liquid at 23° C. and 1000 hPa. Siloxanes (A) are preferablyliquid.

The viscosity of siloxanes (A) employed according to the invention ispreferably between 10 and 20,000 mPas, more preferably between 20 and15,000 mPas, yet more preferably between 30 and 10,000 mPas, mostpreferably between 40 and 8000 mPas.

In a further embodiment, siloxanes (A) are materials at 23° C. and apressure of 1013 hPa that are firm, i.e. no longer flowable, while stillhaving a tacky surface, or they are non-tacky solids having a glasstransition temperature of more than 25° C.

The (A) siloxane resins employed according to the invention are alreadyknown and are obtainable by different methods known to those skilled inthe art, for example by reaction of chlorosilanes with water. U.S. Pat.No. 7,666,969 may be referenced by way of example.

The siloxanes (A) can be used not only in pure form but also in the formof a mixture with a suitable solvent. Use in pure form is preferred.When a solvent is used, the selection depends on the particular organicfunctional group in component (A). It is advantageous to choose solventsthat are not reactive with component (A). Examples of suitable solventsare aromatic solvents, such as toluene, xylene, ethylbenzene or mixturesthereof, and also hydrocarbons and/or mixtures thereof such as, forexample, commercially available isoparaffin mixtures and others.

Preferably, in the (B) siloxanes optionally used, the R⁴ moieties areoverwhelmingly, preferably exclusively, bonded to silicon atoms of unitsof formula (VI) where the f+g+h sum equals 3.

Preferably, component (B) comprises siloxanes consisting of unitsselected from those of the formulae

R⁴ _(f)R⁵ _(g)R⁶ _(h)(R⁷O)_(i)SiO_(1/2) where (f+g+h+i)=3  (VII),

R⁵ _(g)R⁶ _(h)(R⁷O)SiO_(2/2) where (g+h)=1  (VIIIa),

R⁵ _(g)R⁶ _(h)SiO_(2/2) where (g+h)=2  (VIIIb),

R⁵ _(g)R⁶ _(h)(R⁷O)_(i)SiO_(3/2) where (g+h+i)=1  (IX) and

SiO_(4/2)  (V),

where R⁴, R⁵, R⁶, R⁷, f, g, h and i are each as defined above, with theproviso that siloxanes (B) have at least two R⁴ moieties per molecule,not more than 20 mol % of the units conform to formula (IX) or (V) andat least one R⁶ moiety is present per molecule.

The (B) siloxanes optionally employed according to the inventionpreferably contain at least 30 mol % of units of the formula (VIIIb).

More preferably, component (B) comprises siloxanes consisting of atleast two units selected from R⁴R⁵ ₂SiO_(1/2), R⁴R⁵R⁶SiO_(1/2) and R⁴R⁶₂SiO_(1/2) units and also at least one unit selected from R⁵ ₂SiO_(2/2),R⁵R⁶SiO_(2/2) and R⁶ ₂SiO_(2/2) units, where R⁴, R⁵ and R⁶ are each asdefined above.

The (B) siloxanes optionally employed according to the inventionpreferably consist of 3 to 1000 siloxy units, more preferably of 4 to500 units, most preferably of 8 to 100 units.

The (B) siloxanes optionally employed according to the invention mostpreferably comprise linear organopolysiloxanes of the structure

(R⁴R⁵ ₂SiO_(1/2))(R⁶R⁵SiO)₁₋₁₀₀(R⁵ ₂SiO)₀₋₇₀(R⁴R⁵ ₂SiO_(1/2)),

where R⁴, R⁵ and R⁶ are each as defined above and the (R⁶R⁵SiO) unitsand (R⁵ ₂SiO) units may have a random distribution in the molecule.

Examples of (B) siloxanes optionally employed according to the inventionare (Me₂ViSiO_(1/2)) 2 (MePhSiO_(2/2)) 60 (Me₂SiO_(2/2))12/(Me₂ViSiO_(1/2)) 2 (MePhSiO_(2/2)) 10 (Me₂SiO_(2/2)) 2,(Me₂ViSiO_(1/2)) 2 (MePhSiO_(2/2)) and (Me₂ViSiO_(1/2)) 2 (Ph₂SiO_(2/2))where Me is methyl, Vi is vinyl and Ph is phenyl.

The (B) siloxanes optionally employed according to the inventionpreferably have viscosities at 25° C. of preferably 10 to 100,000 mPas,more preferably 100 to 20,000 mPas.

When the compositions of the invention contain component (B), theamounts are preferably from 1 to 200 parts by weight, more preferablyfrom 10 to 150 parts by weight and most preferably from 20 to 120 partsby weight, all based on 100 parts by weight of component (A). In apreferred embodiment, the compositions of the invention contain nocomponent (B).

The (B) siloxanes optionally employed according to the invention arecommercially available products and/or obtainable by chemically routinemethods.

The (C) siloxanes employed according to the invention preferably havetheir R⁸ moieties bonded overwhelmingly, preferably exclusively, tosilicon atoms of units of formula (X) where the k+l+m sum equals 3.

Component (C) preferably comprises siloxanes consisting of unitsselected from those of the formulae

R⁸ _(k)R⁹ _(l)R¹⁰ _(m)(R¹¹O)_(n)SiO_(1/2) where (k+l+m+n)=3  (XI),

R⁹ _(l)R¹⁰ _(m)(R¹¹O)SiO_(2/2) where (l+m)=1  (XIIa),

R⁹ _(l)R¹⁰ _(m)SiO_(2/2) where (l+m)=2  (XIIb),

R⁹ _(l)R¹⁰ _(m)(R¹¹O)_(n)SiO_(3/2) where (l+m+n)=1  (XIII) and

SiO_(4/2)  (V)

where R⁸, R⁹, R¹⁰, R¹¹, k, l, m and n are each as defined above, withthe proviso that siloxanes (C) have at least two R⁸ moieties permolecule, at least one R¹⁰ moiety is present per molecule and at leastone unit of formula (XIII) and/or (V) is present.

The (C) siloxanes employed according to the invention preferably containat least 5 mol % of units of formula (XI), at least 30 mol % of units offormula (XIII) and at most 20 mol % of units of formula (V).

Component (C) more preferably comprises siloxanes consisting of at leastone unit selected from R⁹ ₃SiO_(1/2), R⁸R⁹ ₂SiO_(1/2), R⁹ ₂R¹⁰SiO_(1/2),R⁹R¹⁰ ₂SiO_(1/2), R⁸R⁹R¹⁰SiO_(1/2) and R⁸R¹⁰ ₂SiO_(1/2) units and alsoat least one unit selected from R¹⁰SiO_(3/2), (R¹¹O)SiO_(3/2) andR⁹SiO_(3/2) units, and also optionally units selected from R⁹₂SiO_(2/2), R⁹R¹⁰SiO_(2/2), R¹⁰ ₂SiO_(2/2), R⁹ ₂ (R¹¹O)SiO_(1/2),R⁹R¹⁰(R¹¹O) SiO_(1/2), R⁹ (R¹¹O)SiO_(2/2) and R¹⁰ (R¹¹O)SiO_(2/2) units,where R⁸, R⁹, R¹⁰ and R¹¹ are each as defined above,

with the proviso that at least two R⁸ moieties and also at least one R¹⁰moiety are present per molecule and the optionally contained units R⁹₂SiO_(2/2), R⁹R¹⁰SiO_(2/2) and R¹⁰ ₂SiO_(2/2) may be present incomponent (C) blockwise, as well as in a random distribution.

The (C) resins employed according to the invention preferably have no(OR¹¹) moieties. When, however, they do have (OR¹¹) moieties, forexample as a consequence of the method of synthesis, the amounts arepreferably ≤5 wt %, more preferably ≤5000 weight ppm, specifically ≤1000weight ppm.

The molar fraction of R⁸ moieties as a proportion of the total number ofSi-bonded moieties in siloxane (C) is preferably from 0.1 to 50%, morepreferably from 0.1 to 40%, and most preferably from 1 to 30%.Determination is preferably by ²⁹Si NMR spectroscopy.

The molar fraction of silicon atoms bearing at least one aromatic moietyR¹⁰ as a proportion of the total number of silicon atoms in siloxane (C)is preferably at least 30%, more preferably from 40% to 80%, and mostpreferably from 50% to 75%.

The (C) siloxanes employed according to the invention preferably consistof 3 to 1000 siloxy units, more preferably of 8 to 500 units, mostpreferably of 8 to 100 units.

Preferred examples of component (C) are siloxanes consisting of at leastone unit selected from Me₃SiO_(1/2), ViMe₂SiO_(1/2), Me₂PhSiO_(1/2),MePh₂SiO_(1/2) and ViMePhSiO_(1/2) units and also at least one unitselected from PhSiO_(3/2), HOSiO_(3/2) and MeSiO_(3/2) units and alsooptionally units selected from Me₂SiO_(2/2), MePhSiO_(2/2),Ph₂SiO_(2/2), Me₂(Me₀)SiO_(1/2), Me₂(EtO)SiO_(1/2), Me₂(HO)SiO_(1/2),MePh(Me₀)SiO_(1/2), MePh(EtO)SiO_(1/2), MePh(HO)SiO_(1/2), Ph (Me₀)SiO_(2/2), Ph(EtO)SiO_(2/2) and Ph (HO) SiO_(2/2) units where Me ismethyl, Et is ethyl, Vi is vinyl and Ph is phenyl,

with the proviso that at least 2 vinyl moieties and at least one phenylmoiety are present per molecule and the optionally contained units R⁹₂SiO_(2/2), R⁹R¹⁰SiO_(2/2) and R¹⁰ ₂SiO_(2/2) may be present incomponent (C) blockwise as well as in a random distribution.

Siloxanes (C) preferably have an average molecular weight Mw ofpreferably at least 600 g/mol, more preferably at least 700 g/mol, yetmore preferably at least 800 g/mol, most preferably between 900 and10,000 g/mol, while the polydispersity is preferably at most 20, morepreferably at most 15, yet more preferably at most 10, and mostpreferably at most 8.

The (C) siloxane resins employed according to the invention may be solidor liquid at 23° C. and 1000 hPa, and when liquid, the viscosity of theliquid siloxane resins (C) may be in the range from low to high. Thesiloxanes (C) are preferably of low viscosity.

When the (C) siloxane resins employed according to the invention are oflow viscosity, the viscosity is preferably between 10 and 20,000 mPas,more preferably between 20 and 15,000 mPas, yet more preferably between30 and 10,000 mPas and most preferably between 40 and 8000 mPas, all at25° C.

In a likewise preferred embodiment, siloxanes (C) are materials which at23° C. are highly viscous to firm and have a still tacky surface andglass transition temperatures of more than −20° C., or are non-tackysolids having a glass transition temperature of more than 25° C.

The compositions of the invention preferably contain components (C) inamounts of from 1 to 200 parts by weight, more preferably from 10 to 150parts by weight, and most preferably from 20 to 100 parts by weight, allbased on 100 parts by weight of component (A).

The (C) siloxanes employed according to the invention are obtainable bychemically routine methods.

Component (D), which promotes the addition of Si-bonded hydrogen ontoaliphatic carbon-carbon multiple bonding (hydrosilylation), in thecompositions of the invention may be any hydrosilylation catalyst.

Examples of component (D) are metallic and finely divided platinum,which may be supported on carriers such as silicon dioxide, aluminiumoxide or activated carbon, compounds or complexes of platinum, such asplatinum halides, e.g. PtCl₄, H₂PtCl₆.6H₂O, Na₂PtCl₄.4H₂O,platinum-olefin complexes, platinum-alcohol complexes, platinum-alkoxidecomplexes, platinum-ether complexes, platinum-aldehyde complexes,platinum-ketone complexes, including reaction products formed fromH₂PtCl₆.6H₂O and cyclohexanone, platinum-vinylsiloxane complexes,specifically platinum-divinyltetramethyldisiloxane complexes with orwithout presence of detectable inorganically bound halogen,bis(gamma-picoline)platinum dichloride, trimethylenedipyridineplatinumdichloride, dicyclopentadieneplatinum dichloride,dimethylsulphoxideethyleneplatinum(II) dichloride and also reactionproducts of platinum tetrachloride with olefin and with primary amine orsecondary amine or with primary and secondary amine, such as thereaction product formed from 1-octene-dissolved platinum tetrachloridewith sec-butylamine, or ammonium-platinum complexes, rhodium, palladium,ruthenium and iridium and also their compounds and complexes.Photocurable or UV-curable compositions may utilize, for example,alkylplatinum complexes such as derivatives ofcyclopentadienyltrimethylplatinum(IV),cyclooctadienyldimethylplatinum(II) or diketonato complexes such asbisacetylacetonatoplatinum(II) in order to start the addition reactionwith the aid of light.

These compounds may be encapsulated in a resin matrix.

The (D) catalyst optionally employed according to the inventionpreferably utilizes platinum, its compounds or complexes, morepreferably platinum-divinyltetramethyldisiloxane complexes.

In another preferred embodiment of the invention, the (D) catalystoptionally employed is selected from the group consisting ofcyclopentadienyltrimethylplatinum(IV) and derivatives thereof.

When catalyst (D) is employed, the amount is determined according to thedesired rate of crosslinking and the particular use and also economicconsiderations. The compositions of the invention do preferably containcatalyst (D). The compositions of the invention preferably containcatalysts (D) in amounts resulting in a platinum content of from 0.05 to500 weight ppm (=parts by weight per million parts by weight), morepreferably from 0.5 to 100 weight ppm, most preferably from 1 to 50weight ppm, all based on the total weight of the crosslinkablecomposition.

In addition to the employed components (A), (B), optionally (C) andoptionally (D), the compositions of the invention may contain anyfurther chemical entities also used hitherto in materials crosslinkableby addition reaction other than components (A), (B), (C) and (D),examples being fillers (E), adhesion promoters (F), inhibitors (G),plasticizers (H), additives (K) and organic solvents (L).

The (E) fillers optionally employed in the compositions of the inventionmay comprise any prior art fillers.

Examples of fillers (E) are nonreinforcing fillers, i.e. fillerspreferably having a BET surface area of up to 50 m²/g, such as quartz,diatomaceous earth, calcium silicate, zirconium silicate, talc, kaolin,zeolites, metal oxide powders, such as oxides of aluminium, of titanium,of iron or of zinc, and/or mixed oxides thereof, barium sulphate,calcium carbonate, gypsum, silicon nitride, silicon carbide, boronnitride, glass powder and pulverulent plastic, such as polyacrylonitrilepowder; reinforcing fillers, i.e. fillers having a BET surface area ofmore than 50 m²/g, such as fumed silica, precipitated silica,precipitated chalk, carbon black such as furnace and acetylene blacksand silicon-aluminium mixed oxides of large BET surface area; aluminiumtrihydroxide, fillers in the form of hollow beads such as ceramicmicrobeads, elastic polymeric beads, or glass beads, or fibrous fillers.The recited fillers may be in a hydrophobicized state, for example dueto treatment with organosilanes/organosiloxanes or with stearic acid oretherification of hydroxyl groups into alkoxy groups.

The (E) fillers optionally employed preferably comprise reinforcingfillers having a BET surface area of more than 50 m²/g, such as fumedsilica.

Optionally employed fillers (E) preferably have a moisture content ofpreferably below 1 wt %, more preferably below 0.5 wt %.

When the compositions of the invention do contain fillers (E), theamounts are preferably from 1 to 40 parts by weight, more preferablyfrom 5 to 35 parts by weight and most preferably from 10 to 30 parts byweight, all based on 100 parts by weight of ingredient (A).

In a further embodiment of the invention, the compositions contain from0.01 to 3.0 parts by weight, preferably from 0.05 to 1.0 part by weight,of a fumed silica having a surface area of more than 50 m²/g for thepurpose of controlling the rheological properties.

The compositions of the invention preferably contain no fillers (E).

The (F) adhesion promoters optionally employed in the compositions ofthe invention may comprise any prior art adhesion promoters.

Examples of adhesion promoters (F) are silanes or siloxanes havingmethacryloyloxy or epoxy functions, of which silanes or siloxanes havingepoxy functions are preferable.

When the compositions of the invention contain adhesion promoters (F),the amounts are preferably from 0.01 to 10 parts by weight, morepreferably from 0.05 to 5 parts by weight and most preferably from 0.1to 3 parts by weight, all based on 100 parts by weight of ingredient(A). The compositions of the invention preferably do contain adhesionpromoters (F).

The (G) inhibitors optionally employed may comprise any stabilizers andinhibitors known from the field of addition-crosslinking compositionsand used to precision engineer the pot life and crosslinking rate forthe crosslinkable compositions. Examples of customary inhibitors areacetylenically unsaturated alcohols such as 3-methyl-1-butyn-3-ol,1-ethynylcyclohexan-1-ol, 3,5-dimethyl-1-hexyn-3-ol and3-methyl-1-pentyn-3-ol, polymethylvinylcyclosiloxanes such as1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane, linearvinylsiloxanes such as 1,1,3,3-tetramethyl-1,3-divinyldisiloxane and(vinyl-methyl)-siloxy-dimethyl-siloxy copolymers, trialkyl cyanurates,alkyl maleates such as diallyl maleate and dimethyl maleate, alkylfumarates such as diethyl fumarate and diallyl fumarate, β-ketocompounds such as acetylacetonate, organic hydroperoxides such as cumenehydroperoxide, tert-butyl hydroperoxide and pinane hydroperoxide,organic peroxides, organic sulphoxides, organic amines and amides,phosphines and phosphites, nitriles, triazoles such as benzotriazole,diaziridines and oximes.

When the compositions of the invention contain inhibitors (G), theamounts are preferably from 0.01 to 20 parts by weight, more preferablyfrom 0.01 to 10 parts by weight and most preferably from 0.05 to 2 partsby weight, all based on 100 parts by weight of ingredient (A). Thecompositions of the invention preferably do contain inhibitors (G).

The (H) plasticizers optionally employed may comprise any plasticizersknown from the field of addition-crosslinking materials, examples beingtrialkylsilyl-terminated, linear or branched siloxanes or cyclicsiloxanes free of aliphatically unsaturated moieties and ofsilicon-bonded hydrogen, of which linear and cyclic siloxanes arepreferable.

The compositions of the invention preferably contain no plasticizer (H).

Examples of additives (K) are soluble dyes, organic and inorganicpigments, fluorescent dyes, fungicides, scents, dispersant auxiliaries,rheological additives, corrosion inhibitors, oxidation inhibitors,photoprotectants, thermal stabilizers, flame retardants, agents toinfluence the electrical properties and agents to improve thermalconductivity, light-scattering agents, of which inorganic pigments,organic pigments or fluorescent dyes are preferable.

When the compositions of the invention contain additives (K), theamounts involved are preferably from 0.1 to 30 parts by weight, morepreferably from 1 to 20 parts by weight, and most preferably from 5 to15 parts by weight, all based on 100 parts by weight of ingredient (A).

Examples of solvents (L) are aromatic solvents such as toluene, xylene,ethylbenzene or mixtures thereof and also organic esters of acetic acidsuch as ethyl acetate, butyl acetate, methoxypropyl acetate andhydrocarbons and/or mixtures thereof such as commercially availableisoparaffin mixtures, of which aromatic solvents or isoparaffin mixturesare preferable.

When the compositions of the invention contain solvents (L), the amountsare preferably from 0.1 to 50 parts by weight, more preferably from 1 to30 parts by weight and most preferably from 5 to 20 parts by weight, allbased on 100 parts by weight of ingredient (A). The compositions of theinvention preferably contain no solvents (L).

The compositions of the invention are preferably those containing

(A) siloxanes formed of units of formula (I),optionally (B) siloxanes formed of units of formula (VI),(C) siloxanes formed of units of formula (X),(D) a catalyst to promote the addition of Si-bonded hydrogen ontoaliphatic carbon-carbon multiple bonds,optionally (E) fillers,optionally (F) adhesion promoters,optionally (G) inhibitors,optionally (H) plasticizers,optionally (K) additives, andoptionally (L) solvents.

In a further preferred embodiment, the compositions of the inventionpreferably comprise those containing

(A) siloxanes formed of units of formula (I),

optionally (B) siloxanes formed of units of formula (VI),(C) siloxanes formed of units of formula (X),(D) a catalyst to promote the addition of Si-bonded hydrogen ontoaliphatic carbon-carbon multiple bonds,optionally (E) fillers,(F) adhesion promoters,optionally (G) inhibitors,optionally (H) plasticizers,optionally (K) additives, andoptionally (L) solvents.

The compositions of the invention more preferably comprise thosecontaining

(A) siloxanes formed of units of formula (I),(C) siloxanes formed of units of formula (X),(D) a catalyst to promote the addition of Si-bonded hydrogen ontoaliphatic carbon-carbon multiple bonds,(F) adhesion promoters,optionally (G) inhibitors,optionally (H) plasticizers,optionally (K) additives, andoptionally (L) solvents.

In a further preferred embodiment, the compositions of the inventioncomprise those containing

(A) siloxanes formed of units of formula (I),(B) siloxane formed of units of formula (VI),(C) siloxanes formed of units of formula (X),(D) a catalyst to promote the addition of Si-bonded hydrogen ontoaliphatic carbon-carbon multiple bonds,(F) adhesion promoters,optionally (G) inhibitors,optionally (H) plasticizers,optionally (K) additives, andoptionally (L) solvents.

In a further preferred embodiment, the compositions of the inventioncomprise those containing

(A) siloxanes formed of units of formula (I),optionally (B) siloxanes formed of units of formula (VI),(C) siloxanes formed of units of formula (X),(D) a catalyst to promote the addition of Si-bonded hydrogen ontoaliphatic carbon-carbon multiple bonds, which is selected from the groupof platinum-vinylsiloxane complexes,optionally (E) fillers,(F) adhesion promoters,optionally (G) inhibitors,optionally (H) plasticizers,optionally (K) additives, andoptionally (L) solvents.

In a further preferred embodiment, the compositions of the inventioncomprise those containing

(A) siloxanes formed of units of formula (I),optionally (B) siloxanes formed of units of formula (VI), (C) siloxanesformed of units of formula (X),(D) a catalyst to promote the addition of Si-bonded hydrogen ontoaliphatic carbon-carbon multiple bonds, which is selected from the groupconsisting of cyclopentadienyltrimethylplatinum(IV) and its derivatives,optionally (E) fillers,(F) adhesion promoters,optionally (G) inhibitors,optionally (H) plasticizers,optionally (K) additives, andoptionally (L) solvents.

Components (A) to (L) aside, the compositions of the inventionpreferably contain no further ingredients.

The components employed according to the invention may each comprise amixture of at least two species of such a component as well as onespecies of a particular component.

The compositions according to the invention are preferably flowable,capable of being processed using commercially available meteringequipment and colourless and transparent after vulcanization.

The compositions of the invention may—in a way which more particularlydepends on the filler content and the viscosity of the ingredients—be oflow viscosity and pourable, have a pasty consistency, be pulverulent orelse constitute pliant high-viscosity materials, similarly to thecompositions frequently referred to as RTV-1, RTV-2, LSR and HTV bythose skilled in the art. Preferably, the compositions are of lowviscosity and may conform to properties of compositions referred to asRTV-2 by those skilled in the art.

The compositions of the invention are obtainable in any conventionalmanner, for instance by methods and mixing processes of the typecustomary in the manufacture of addition-crosslinking compositions.

The present invention further provides a process for producing thecompositions of the invention by mixing the individual components in anyorder.

This mixing together may be carried out at room temperature and thepressure of the ambient atmosphere, i.e. about 900 to 1100 hPa. Ifdesired, however, this mixing together may also be carried out at highertemperatures, for example at temperatures in the range from 30 to 130°C. It is further possible to mix transiently or constantly under reducedpressure, for example at from 30 to 500 hPa absolute pressure, in orderto remove volatile compounds and/or air.

When, in one embodiment, component (D) is a catalyst whereby theaddition reaction is started with the aid of light, the mixing step ofthe invention is preferably carried out in the absence of light having awavelength range of from 190 to 500 nm.

The process of the invention may be carried out in a continuous manneror batchwise.

In a preferred embodiment of the process according to the invention,catalyst (D) is uniformly mixed with a mixture of (A), optionally (B),(C), optionally (G) and optionally (F). The (D) catalyst employedaccording to the invention may be incorporated by itself, as a solutionin a suitable solvent, or as a batch distributed uniformly with a smallamount of a siloxane such as, for example, (C) or, if employed incertain embodiment, in component (B) or component (G).

The mixing apparatus used may be any suitable prior art apparatuses, forexample dissolvers or planetary mixers.

The compositions of the invention may comprise not only one-componentsilicone compositions but also two-component silicone compositions. Inthe latter case, the component containing catalyst (D) is prepared bymixing catalyst (D) with (C) and optionally (B), optionally (G) andoptionally (F) in a uniform manner, whereas the component containing thesilicon-bonded hydrogen either consists of (A) only or is prepared byuniform mixing of component (A) with optionally (B), (C), optionally (G)and optionally (F).

When the compositions of the invention comprise one-component siliconecompositions, the temperature of the compositions is preferablymaintained at below 50° C., more preferably at from 10 to 30° C., duringthe mixing of the components in order to prevent a premature onset ofthe crosslinking reaction.

The materials of the invention which are crosslinkable by addition ofSi-bonded hydrogen onto aliphatic multiple bonding may be crosslinkedunder the same conditions as the prior art compositions crosslinkable byhydrosilylation reaction.

The compositions of the invention are preferably processed usingcommercially available mixing and metering equipment, preferably attemperatures of between 15 and 50° C., preferably by metering into openmoulds or directly onto the component parts desired, with subsequentcrosslinking at the pressure of the ambient atmosphere, i.e. about 900to 1100 hPa.

Crosslinking is preferably effected thermally.

More particularly, crosslinking is effected in the presence of acatalyst to promote the addition reaction upon activation by heating.

The crosslinking temperature is preferably in the range of from 0 to200° C., in particular from 10 to 150° C. Crosslinking periods arepreferably between 1 minute and 10 hours, more preferably between 10minutes and 5 hours, most preferably between 30 minutes and 3 hours.

In another embodiment, crosslinking is effected at pressures of the typecustomary in an injection moulding machine, i.e. about 200,000 hPa.Temperatures in this embodiment are preferably between 50 and 200° C.,in particular between 120 and 180° C. Crosslinking periods are between 1second and 10 minutes, preferably between 5 seconds and 2 minutes.

In a further embodiment wherein the composition of the inventioncontains by way of component (D) a catalyst whereby the additionreaction is started with the aid of light, the composition is preferablycrosslinked after irradiation in the UV-VIS range of the electromagneticspectrum, i.e. between 190 and 800 nm, preferably between 250 and 500nm. Useful sources of light include any known appropriate light sourcesand combinations of light sources with filters, for example mercuryvapour lamps, doped mercury vapour lamps, xenon discharge lamps, otherdischarge lamps, LED light sources or lasers.

The present invention further provides shaped articles obtained bycrosslinking the compositions of the invention.

The shaped articles of the invention may comprise any desired shapedarticles, for example gaskets, press mouldings, extruded profiles,extruded strands, coatings, impregnations, encapsulation, lenses,articles for light conductance, prisms, polygonal structures, laminatelayers or adhesive layers, preferably encapsulation, lenses and articlesfor light conductance.

The shaped articles of the invention have hardnesses which arepreferably in the range from Shore A 20 to Shore D 80, more preferablyin the range from Shore A 70 to Shore D 80. The shaped articles of theinvention are preferably colourless and highly transparent withtransmissions preferably >90% between 400 and 800 nm, measured by UV-VISspectroscopy. The shaped articles of the invention preferably evincelittle, and more preferably, no yellowing under thermal stress. Shapedarticles according to the invention have refractive indices n_(D) ²⁵ ofpreferably >1.43, more preferably >1.46, yet more preferably >1.50, andmost preferably >1.52.

The compositions of the invention and also the crosslinked productsobtained therefrom according to the invention are useful for anypurposes hitherto also utilizing elastomerically crosslinkable siloxanecompositions and elastomers, respectively. This includes, for example,the silicone coating/impregnation of any desired substrates, theproduction of moulded parts, for example by injection moulding,extrusion, vacuum extrusion, cast moulding and compression moulding, andcasts, use as sealants, and embedding and encapsulation compounds.

A preferred use of the composition of the invention is its use forencapsulation of optical semiconductor elements such as LEDs. In apreferred embodiment thereof, the composition of the invention ismetered, for example with a customary metering rig, onto thesemiconductor element and then vulcanized. Different chip designs can beused therein for the semiconductor elements (known as LED packages),such as SMD (surface mounted design) packages, COB (Chip on Board)packages, MCOB (Multiple Chip on Board) and others.

The compositions of the invention have the advantage of being easy toproduce.

The compositions of the invention have the advantage of a very highstability in storage and a high rate of crosslinking.

The compositions of the invention further have the advantage of evincingan excellent profile of adherence.

The compositions of the invention further have the advantage of beingeasy to process.

The compositions of the invention have the advantage of being simple tovary while meeting the above-shown requirements.

The compositions of the invention further have the advantage of meetingthe requirements for LED encapsulation compounds, having goodprocessability and being curable into optically high-transparencyvulcanizates.

The process for producing the siloxane compositions in the manner of theinvention has the advantage of being simple to carry out.

Optical component parts such as LEDs encapsulated with the compositionsof the invention before these were crosslinked surprisingly survive thealternating temperature test to, preferably, at least 100 cycles, morepreferably at least 300 cycles, and most preferably at least 500 cycles.

Optical component parts such as LEDs encapsulated with the compositionsof the invention before these were crosslinked advantageously have animproved resistance to sulphur-containing gases.

Optical component parts such as LEDs encapsulated with the compositionsof the invention before these were crosslinked advantageously haveimproved light efficiencies over the prior art.

Unless otherwise stated, the examples hereinafter are carried out at apressure of the ambient atmosphere, i.e. for example at 1000 hPa, and atroom temperature, i.e. at about 23° C., and/or at a temperature as isestablished when the reactants are added together at room temperaturewithout additional heating or cooling, and also at a relative humidityof about 50%. Parts and percentages unless otherwise stated are furtherall by weight.

Chemical entities are characterized in the present text by indication ofdata obtained using instrumental analysis. The underlying measurementsare carried out either in accordance with publicly accessible standardsor determined using specifically developed methods. To safeguard theclarity of the teaching disclosed, the methods used are here specified:

Viscosity:

Viscosities unless otherwise stated are determined on an MCR302rheometer from Anton Paar, D-Ostfildern as per DIN EN ISO 3219 inrotation with a plate-cone system of measurement. The measurements arecarried out in the Newtonian domain of the samples. Where a sampleexhibits non-Newtonian behaviour, the rate of shear is also reported.Unless otherwise indicated, all reported viscosities relate to 25° C.and standard pressure at 1013 mbar.

Refractive Index:

Refractive indices are determined in the wavelength range of visiblelight, unless otherwise stated at 589 nm and 25° C. (n_(D) ²⁵) andstandard pressure at 1013 mbar as per the standard DIN 51423. Abberefractometers from A. Krüss Optronics, D-Hamburg and from Atago, Japan,type DR-M2 were used.

Molecular Compositions:

Molecular compositions are determined using nuclear magnetic resonancespectroscopy (regarding the terminology see ASTM E 386: High-ResolutionNuclear Magnetic Resonance (NMR) spectroscopy: terms and symbols), bymeasuring the ¹H nucleus and the ²⁹Si nucleus.

Description of 1H NMR Measurement

-   Solvent: CDCl₃, 99.8% d-   Sample concentration: about 50 mg/1 ml CDCl₃ in 5 mm NMR vial

Measurement without admixture of TMS, spectral referencing of residualCHCl₃ in CDCl₃ at 7.24 ppm

-   Spectrometer: Bruker Avance I 500 or Bruker Avance HD 500-   Probe head: 5 mm BBO probe head or SMART probe head (from Bruker)

Measurement parameters:

Pulprog=zg30

TD=64 k

NS=64 or 128 (depending on the sensitivity of the probe head)

SW=20.6 ppm AQ=3.17 s D1=5 s SFO1=500.13 MHz O1=6.175 ppm

Processing parameters:

SI=32 k WDW=EM LB=0.3 Hz

Depending on the spectrometer type used, individual adjustments of themeasurement parameters may be required.

Description of 29Si NMR Measurement

-   Solvent: C6D6 99.8% d/CCl4 1:1 v/v with 1 wt % of Cr(acac)₃ as    relaxation reagent-   Sample concentration: about 2 g/1.5 ml solvent in 10 mm NMR vial-   Spectrometer: Bruker Avance 300-   Probe head: 10 mm 1H/13C/15N/29Si glass-free QNP probe head (from    Bruker)

Measurement parameters:

Pulprog=zgig60

TD=64 k

NS=1024 (depending on probe head sensitivity)

SW=200 ppm AQ=2.75 s D1=4 s SFO1=300.13 MHz O1=−50 ppm

Processing parameter:

SI=64 k WDW=EM LB=0.3 Hz

Depending on the spectrometer type used, individual adjustments of themeasurement parameters may be required.

Molecular Weight Distributions:

Molecular weight distributions are determined as Mw weight averages andMn number averages, using the method of gel permeation chromatography(GPC or Size Exclusion Chromatography (SEC)) with polystyrene standardand refractive index (RI) detector. Unless otherwise noted, THF is usedas mobile phase and DIN 55672-1 applies. Polydispersity is the Mw/Mnquotient.

Glass Transition Temperatures:

Glass transition temperature is determined by differential scanningcalorimetry (DSC) to DIN 53765, in a perforated crucible at a heatingrate of 10 K/min on a DSC 1 calorimeter from Mettler Toledo,CH-Greifensee.

Shore Hardnesses:

Shore hardnesses A and D are determined to DIN (German IndustrialSpecification) 53505 (as at August 2000) on hardness-measuringinstruments from Bareiss, D-Oberdischingen (models HPE II Shore A andShore D), respectively.

Alternating Temperature Test:

The alternating temperature tests on vulcanizates and/or operationalencapsulated component parts are carried out using instruments fromEspec, Japan (Thermal Shock Chamber TSE-11, Elevator Type). Unlessotherwise stated, the thermocycles have a bottom temperature of −45° C.and a top temperature of 125° C. The samples are maintained at eithertemperature for 15 minutes. One cycle thus takes 30 minutes.

Resistance to Sulphur-Containing Gases:

The water-covered base of a glass vessel has a dish containing K₂Splaced onto it such that the K₂S does not come into contact with thewater. The operational component parts (LEDs for example) are placed inthe gas space above the dish containing K₂S and the vessel is sealed.The glass vessel is heated to 85° C. in a water bath. Measurements onthe component parts are typically carried out at intervals of 8 h. Theprocedure for the measurements is as follows: first the light efficiencyof the untreated LEDs is measured. Then, the LEDs are exposed asdescribed above to the conditions in the above-described glass vesselcontaining K₂S. Thereafter, the light efficiency of the LEDs is measuredagain and compared with the initial value. This may then be followed byfurther cycles of exposure in the glass vessel and subsequentmeasurement of the light efficiency.

Light Efficiency:

The light efficiencies are determined using an instrument fromInstrument Systems, Japan, of the type Compact Array Spectrometer CAS140CT on an Ulbricht sphere of type ISP 250 (250 mm internal diameter)in accordance with CIE 127 for radiant power measurements on LEDs.

Hereinafter

Ph is phenyl=C₆H₅—,Vi is vinyl=CH₂═CH—, andMe is methyl=CH₃—.

Preparing an Si—H and Si-Vi Bifunctional Phenyl-Type Resin of BalancedFunctionality (A1)

The apparatus used for carrying out the reaction is a 1 l 4-neck glassflask equipped with an outlet, a KPG stirrer, an intensive condenser anda metering vessel (dropping funnel). A 300 g quantity of completelyion-free water is introduced into the glass flask. A magnetic stirrer isused to mix 60 g (0.5 mol) of vinyldimethylchlorosilane (molecularweight 120.5 g/mol), 135 g (0.63 mol) of phenyltrichlorosilane(molecular weight 211.5 g/mol) and 30 g (0.31 mol) ofdimethylchlorosilane (molecular weight 94 g/mol) in a 1 l glass beakerand then the mixture is transferred into the metering vessel.

The chlorosilane mixture is metered into the initial water charge over 2hours, during which the temperature rises from 21.3° C. to 46.0° C. Oncompletion of the metered addition, the mixture is subsequently stirredfor 1 hour longer without heating or cooling. Thereafter, a further 19 g(0.2 mol) of dimethylchlorosilane are introduced into the meteringvessel and admixed over a period of 10 minutes. On completion of themetered addition the temperatures is 32° C. The mixture is subsequentlystirred for 20 minutes. A two-phase reaction mixture is obtained. Thebottom phase is the aqueous phase, which is acidic due to hydrochloricacid and is discharged from the flask. A 500 g quantity of completelyion-free water is added to the remaining product phase before heating to60° C. In the two-phase mixture obtained, the top phase is the aqueousphase, which is again separated off. The washing procedure is repeatedaltogether three times. Then, 15 g of Seitz EF filter aid are admixed tothe product phase, before stirring for 15 minutes and filtration with apressure filter apparatus through a Seitz K 100 filter plate.

The filtrate is heated for 2 hours in a rotary evaporator at 160° C. and10 mbar pressure to obtain 110 g of a slightly cloudy product having aviscosity of 133 mm²/s.

The resulting resin (A1) is shown by SEC (mobile phase THF) to have amolecular weight of Mw=1900 g/mol and Mn=1000 g/mol. The silanol contentis determined by ¹H NMR as 195 ppm.

The vinyl content is 2.64 mmol/g, and the Si-bonded hydrogen content is2.54 mmol/g.

According to ²⁹Si NMR, the molar composition is:

ViMe₂SiO_(1/2): 27.4%,Me₂ (H)SiO_(1/2): 26.3%,Me₂SiO_(2/2): 1.2%,Ph(OH)₂SiO_(1/2): 0.0%,

Ph(OH) SiO_(2/2): 8.3% and PhSiO_(3/2): 36.8%.

The product is free of alkoxysilyl groups.

Preparing an Si—H and Si-Vinyl Bifunctional Phenyl-Type Resin whereSiH/Vi=1.15 (A2)

The procedure is similar as for the preparation of resin (A1).

The apparatus used is a 4 l flask. The amounts used are chosen asfollows:

completely ion-free water: 1350 gvinyldimethylchlorosilane (molecular weight 120.5 g/mol): 188.9 g (1.57mol)phenyltrichlorosilane (molecular weight 211.5 g/mol): 674.85 g (3.19mol)dimethylchlorosilane in the chlorosilane mixture: 115.48 g (1.23 mol)dimethylchlorosilane for later dosage: 73.22 g (0.78 mol).

The washings are done at 45° C. The product is devolatilized in a rotaryevaporator at 100° C. and 6 mbar to obtain 470 g of a clear producthaving a viscosity of 548 mPas and a refractive index n_(D) ²⁵ of 1.502.

The resulting resin (A2) is shown by SEC (mobile phase THF) to have amolecular weight of Mw=1700 g/mol and Mn=1100 g/mol. The silanol contentis determined by ¹H NMR as 394 ppm.

The vinyl content is 2.15 mmol/g, and the Si-bonded hydrogen content is2.52 mmol/g.

According to ²⁹Si NMR, the molar composition is:

ViMe₂SiO_(1/2): 23.0%,Me₂(H)SiO_(1/2): 27.2%,

Ph(OH)SiO_(2/2): 9.8% and PhSiO_(3/2): 40.0%.

The product is free of alkoxysilyl groups.

Preparing an Si—H and Si-Vinyl Bifunctional Phenyl-Type Resin whereSiH/Vi=2.3 (A3)

The procedure is similar as for the preparation of resin (A1). Theapparatus used is a 4 l flask. The amounts used are chosen as follows:

completely ion-free water: 1320 gvinyldimethylchlorosilane: 107.38 g (0.89 mol)phenyltrichlorosilane (molecular weight 211.5 g/mol): 674.85 g (3.19mol)dimethylchlorosilane in the chlorosilane mixture: 156.63 g (1.65 mol)dimethylchlorosilane for later dosage: 96.00 g (1.01 mol).

The washings are done at 45° C. The product is devolatilized in a rotaryevaporator at 100° C. and 6 mbar to obtain 413 g of a clear producthaving a viscosity of 861 mPas and a refractive index n_(D) ²⁵ of 1.504.

The resulting resin (A3) is shown by SEC (mobile phase THF) to have amolecular weight of Mw=2000 g/mol and Mn=1200 g/mol. The silanol contentis determined by ¹H NMR as 680 ppm.

The vinyl content is 1.3 mmol/g, and the Si-bonded hydrogen content is3.18 mmol/g.

According to ²⁹Si NMR, the molar composition is:

ViMe₂SiO_(1/2): 14.4%,Me₂ (H)SiO_(1/2): 34.1%,

Ph (OH) SiO_(2/2): 10.2% and PhSiO_(3/2): 41.3%.

The product is free of alkoxysilyl groups.

Preparing an Si—H and Si-Vinyl Bifunctional Phenyl-Type Resin whereSiH/Vi=0.15 (A4)

The procedure is similar as for the preparation of resin (A1).

The apparatus used is a 1 l flask. The amounts used are chosen asfollows:

completely ion-free water: 255 gvinyldimethylchlorosilane: 60.00 g (0.497 mol)phenyltrichlorosilane: 135.36 g (0.64 mol)dimethylchlorosilane in the chlorosilane mixture: 5.23 g (0.055 mol).

The washings are done at 45° C. The product is devolatilized in a rotaryevaporator at 100° C. and 6 mbar to obtain 84 g of a clear producthaving a viscosity of 1390 mPas and a refractive index n_(D) ²⁵ of1.511.

The resulting resin (A4) is shown by SEC (mobile phase THF) to have amolecular weight of Mw=1900 g/mol and Mn=1200 g/mol. The silanol contentis determined by ¹H NMR as 3373 ppm.

The vinyl content is 3.33 mmol/g, and the Si-bonded hydrogen content is0.46 mmol/g.

According to ²⁹Si NMR, the molar composition is:

ViMe₂SiO_(1/2): 38.6%,Me₂ (H) SiO_(1/2): 5.8%,

Ph(OH)SiO_(2/2): 20.2% and PhSiO_(3/2): 35.4%.

The product is free of alkoxysilyl groups.

Preparing an Si—H and Si-Vinyl Bifunctional Phenyl-Type Resin whereSiH/Vi=6.65 (A5)

The procedure is similar as for the preparation of resin (A1).

The amounts used are chosen as follows:

completely ion-free water: 260 gvinyldimethylchlorosilane: 6.87 g (0.057 mol)phenyltrichlorosilane: 135.36 g (0.64 mol)dimethylchlorosilane in the chlorosilane mixture: 48.52 g (0.513 mol).

The washings are done at 45° C. The product is devolatilized in a rotaryevaporator at 100° C. and 6 mbar to obtain 74 g of a clear producthaving a viscosity of 611 mPas and a refractive index n_(D) ²⁵ of 1.506.

The resulting resin (A5) is shown by SEC (mobile phase THF) to have amolecular weight of Mw=1600 g/mol and Mn=1100 g/mol. The silanol contentis determined by ¹H NMR as 1262 ppm.

The vinyl content is 0.47 mmol/g, and the Si-bonded hydrogen content is3.97 mmol/g.

According to ²⁹Si NMR, the molar composition is:

ViMe₂SiO_(1/2): 6.0%,Me₂ (H) SiO_(1/2): 40.7%,

Ph(OH)SiO_(2/2): 14.9% and PhSiO_(3/2): 38.4%.

The product is free of alkoxysilyl groups.

Preparing an Si—H and Si-Vinyl Bifunctional Phenyl-Type Resin whereSiH/Vi=2.10 (A6)

The procedure is similar as for the preparation of resin (A1).

The amounts used are chosen as follows:

completely ion-free water: 270.00 gvinyldimethylchlorosilane: 18.89 g (0.157 mol)phenyltrichlorosilane: 134.97 g (0.638 mol)silane PM2: 26.73 g (0.156 mol)dimethylchlorosilane in the chlorosilane mixture: 23.10 g (0.24 mol)dimethylchlorosilane for later dosage: 14.64 g (0.15 mol).

The washings are done at 45° C. The product is devolatilized in a rotaryevaporator at 100° C. and 6 mbar to obtain 89 g of a clear producthaving a viscosity of 314 mPas and a refractive index n_(D) ²⁵ of 1.512.

The resulting resin (A6) is shown by SEC (mobile phase THF) to have amolecular weight of Mw=1700 g/mol and Mn=1000 g/mol. The silanol contentis determined by ¹H NMR as 474 ppm.

The vinyl content is 1.00 mmol/g, and the Si-bonded hydrogen content is2.48 mmol/g.

According to ²⁹Si NMR, the molar composition is:

ViMe₂SiO_(1/2): 12.2%,Me₂(H) SiO_(1/2): 27.1%,Me₂PhSiO_(1/2): 11.6%,

Ph (OH) SiO_(2/2): 11.9% and PhSiO_(3/2): 37.2%.

The product is free of alkoxysilyl groups.

Preparing an Si-Vinyl Functional Phenyl-Type Resin (C₁)

700 g of phenyltriethoxysilane (2.91 mol), 61.6 g ofdimethyldiethoxysilane (0.415 mol) and 77.6 g of1,3-divinyl-1,1,3,3-tetramethyldisiloxane (0.416 mol) are mixedhomogeneously in a 2 l flask. To the mixture is added, under agitation,550 g of water followed by 3.0 g of 20% HCl. The mixture is heated andrefluxed for 2 h under agitation. After cooling, 4.5 g of 20% aqueoussodium hydroxide solution are admixed before refluxing for 30 min. At apressure of 50 mbar, ethanol formed is distilled off and 800 ml oftoluene are admixed. The aqueous phase is separated off and the organicphase is washed three times with 500 ml of water. The organic phase isdried over magnesium sulphate and the product is devolatilized in arotary evaporator at 140° C. and 5 mbar to obtain 470 g of a clear, veryhighly viscous product having a glass transition temperature of 5° C.

The resulting resin (C1) is shown by SEC (mobile phase THF) to have amolecular weight of Mw=2000 g/mol and Mn=1400 g/mol. The vinyl contentis 1.48 mmol/g.

According to ²⁹Si NMR, the molar composition is:

ViMe₂SiO_(1/2): 17.9%,Me₂SiO_(2/2): 11.0%Ph(OR)SiO_(2/2): 18.0% (R═H: 3%; R=ethyl: 15%) and

PhSiO_(3/2): 53.1%.

Preparing an Si-Vinyl Functional Phenyl-Type Resin (C2)

600 g of phenyltrichlorosilane (2.84 mol) and 113 g (0.936 mol) ofvinyldimethylchlorosilane are mixed homogeneously and added dropwise at50° C. to a mixture of 600 g of water, 310 g of toluene and 190 g ofethyl acetate. The mixture is subsequently refluxed for two hours. Aftercooling the mixture down to room temperature, 700 ml of toluene areadmixed, the aqueous phase is separated off and the organic phase iswashed twice with 1 l of water and then dried over magnesium sulphateand the solvent is distilled off.

This gives 450 g of a clear, very highly viscous product having a glasstransition temperature of 10° C.

The resulting resin (C2) is shown by SEC (mobile phase THF) to have amolecular weight of Mw=2200 g/mol and Mn=1600 g/mol.

The vinyl content is 1.85 mmol/g.

According to ²⁹Si NMR, the molar composition is:

ViMe₂SiO_(1/2): 31.2%,Ph(OR)SiO_(2/2): 30.2% (R═H: 5%; R=ethyl 25%) and

PhSiO_(3/2): 38.6%.

Preparing an Si-Vinyl Functional Phenyl-Type Resin (C3)

A 2 l flask is charged with 700 g of phenyltriethoxysilane (2.91 mol),217.6 g (1.6 mol based on PhMeSiO_(1/2) units) of a short-chainα,ω-silanol-functional phenylmethyl oil having the average composition:(HO)PhMeSiO-[PhMeSiO]₄-PhMeSi—OH, which has an average molecular weightof Mw=800 g/mol at Mn=700 g/mol and a viscosity of 503 mPas at 25° C.and standard pressure at 1013 mbar, and 77.6 g of1,3-divinyl-1,1,3,3-tetramethyldisiloxane (0.416 mol) are mixedhomogeneously. To the mixture is added, under agitation, 550 g of waterfollowed by 3.0 g of 20% HCl. The mixture is heated and refluxed for 2 hunder agitation. After cooling, 4.5 g of 20% aqueous sodium hydroxidesolution are admixed before refluxing for 30 min. At a pressure of 50mbar, ethanol formed is distilled off and 800 ml of toluene are admixed.The aqueous phase is separated off and the organic phase is washed threetimes with 500 ml of water. The organic phase is dried over magnesiumsulphate and the product is devolatilized in a rotary evaporator at 140°C. and 5 mbar to obtain 595 g of a clear, very highly viscous product.

The resulting resin (C3) is shown by SEC (mobile phase THF) to have amolecular weight of Mw=2300 g/mol and Mn=1500 g/mol. The vinyl contentis 1.1 mmol/g.

According to ²⁹Si NMR, the molar composition is:

ViMe₂SiO_(1/2): 15.2%,Me₂SiO_(2/2): 30.9%Ph(OR)SiO_(2/2): 13% (R═H: 4%; R=ethyl: 9%) and

PhSiO_(3/2): 40.9%.

EXAMPLES

The formulations are prepared as follows in the examples which follow:

The formulations are prepared by preparing homogeneous mixtures of theparticular reported components using a DAC 150 FV type Speedmixer fromHauschild and subsequent degassing of the sample with an oil diffusionpump or on a planetary mixer from Thinky Corporation, Japan, typeAWATORI RENTARO Model ARV-310 by simultaneous evacuation.

Unless otherwise stated, the degassed mixtures are poured into opensteel moulds having a diameter of 35 mm and a height of 6 mm and allowedto vulcanize at 150° C. in a circulating air drying cabinet. Thevulcanization period is reported with the particular formulation.

Example 1

In a planetary mixer, 80 parts of resin (A2) are mixed with 20 parts ofresin (C1) and 0.0002 part (based on platinum) of aplatinum-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex. The mixtureis vulcanized at 150° C. for 1 h. The vulcanizate has a Shore D hardnessof 58.

Example 2

In a planetary mixer, 45 parts of resin (A3) are mixed with 55 parts ofresin (C1) and 0.0002 part (based on platinum) of aplatinum-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex. The mixtureis vulcanized at 150° C. for 1 h. The vulcanizate has a Shore D hardnessof 65.

Example 3

In a planetary mixer, 35 parts of resin (A5) are mixed with 65 parts ofresin (C1) and 0.0002 part (based on platinum) of aplatinum-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex. The mixtureis vulcanized at 150° C. for 1 h. The vulcanizate has a Shore D hardnessof 70.

Example 4

In a planetary mixer, 60 parts of resin (A2) are mixed with 40 parts ofresin (C1) and 0.0002 part (based on platinum) of aplatinum-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex. The mixtureis vulcanized at 150° C. for 1 h. The vulcanizate has a Shore D hardnessof 30.

Example 5

In a planetary mixer, 70 parts of resin (A2) are mixed with 30 parts ofresin (C3) and 0.0002 part (based on platinum) of aplatinum-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex. The mixtureis vulcanized at 150° C. for 1 h. The vulcanizate has a Shore D hardnessof 45.

Example 6

In a planetary mixer, 60 parts of resin (A2) are mixed with 30 parts ofresin (C1), 10 parts of a vinyl-terminatedpolydimethylphenylmethylsiloxane having the composition(Me₂ViSiO_(1/2))₂(MePhSiO_(2/2))₆₀(Me₂SiO_(2/2))₁₂ (refractive indexn_(D) ²⁵=1.538, viscosity η=7800 mPas) and 0.0002 part (based onplatinum) of a platinum-1,3-divinyl-1,1,3,3-tetramethyldisiloxanecomplex. The mixture is vulcanized at 150° C. for 1 h. The vulcanizatehas a Shore D hardness of 40.

Example 7

In a planetary mixer, 60 parts of resin (A2) are mixed with 40 parts ofresin (C1) and 0.002 part (based on platinum) ofmethylcyclopentadienyltrimethylplatinum(IV). The mixture is degassed,poured into an open steel mould having a diameter of 35 mm and a heightof 6 mm and irradiated with an iron irradiator (“D-bulb”) from Hanle,Gräfelfing, Germany at 140 mW/cm² for 15 seconds. The vulcanizate has aShore D hardness of 50.

Example 8

In a planetary mixer, 60 parts of resin (A2) are mixed with 30 parts ofresin (C1), 10 parts of a vinyl-terminatedpolydimethylphenylmethylsiloxane having the composition(Me₂ViSiO_(1/2))₂(MePhSiO_(2/2))₆₀(Me₂SiO_(2/2))₁₂ (refractive indexn_(D) ²⁵=1.538, viscosity η=7800 mPas), 0.5 part of(3-glycidoxypropyl)trimethoxysilane and 0.0002 part (based on platinum)of a platinum-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex. Themixture is vulcanized at 150° C. for 1 h. The vulcanizate has a Shore Dhardness of 40.

Comparative Example 1

In a planetary mixer, 70 parts of resin (C2) are mixed with 10 parts ofa vinyl-terminated polydimethylphenylmethylsiloxane having thecomposition (Me₂ViSiO_(1/2))₂(MePhSiO_(2/2))₆₀(Me₂SiO_(2/2))₁₂(refractive index n_(D) ²⁵=1.538, viscosity 1=7800 mPas), 20 parts of1,1,5,5-tetramethyl-3,3-diphenyltrisiloxane and 0.0002 part (based onplatinum) of a platinum-1,3-divinyl-1,1,3,3-tetramethyldisiloxanecomplex. The mixture is vulcanized at 150° C. for 2 h. The vulcanizatehas a Shore A hardness of 60.

Comparative Example 2

In a planetary mixer, 65 parts of resin (C2) are mixed with 35 parts of1,1,5,5-tetramethyl-3,3-diphenyltrisiloxane and 0.0002 part (based onplatinum) of a platinum-1,3-divinyl-1,1,3,3-tetramethyldisiloxanecomplex. The mixture is vulcanized at 150° C. for 4 h. The vulcanizatehas a Shore D hardness of 38.

Example 9

In a planetary mixer, 50 parts of resin (A2) are mixed with 50 parts ofresin (C1), 0.5 part of (3-glycidoxypropyl)trimethoxysilane and 0.0002part (based on platinum) of aplatinum-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex. The mixtureis vulcanized at 150° C. for 1 h. The vulcanizate has a Shore D hardnessof 68.

1.-11. (canceled)
 12. A compositions comprising: (A) at least oneorganopolysiloxane comprising at least 3 units of the formulaR¹ _(a)R² _(b)R³ _(c)H_(d)(RO)_(e)SiO_((4-a-b-c-d-e)/2)  (I), where R¹each independently are monovalent, SiC-bonded, optionally halogen- orcyano-substituted hydrocarbyl moieties with aliphatic carbon-carbonmultiple bonding, R² each independently are monovalent, SiC-bonded,optionally halogen- or cyano-substituted, saturated hydrocarbylmoieties, R³ each independently are monovalent SiC-bonded aromaticmoieties, R each independently are hydrogen or monovalent, optionallysubstituted hydrocarbyl moieties which are optionally interrupted byheteroatoms, a is 0, 1, 2 or 3, b is 0, 1, 2 or 3, c is 0, 1, 2 or 3, dis 0, 1 or 2, and e is 0, 1 or 2, with the proviso that the a+b+c+d+esum is not more than 3, the sum total of Si-bonded hydrogen atoms and R¹moieties per molecule is at least 3, the a+b+c+d sum is equal to 0 or 1in at least 10 mol % of the units of formula (I), c is other than 0 inat least one unit, and the ratio of Si-bonded hydrogen atoms toSi-bonded R¹ moieties in the siloxane (A) is from 0.1 to 9, optionally(B) organopolysiloxanes comprising units of the formulaR⁴ _(f)R⁵ _(g)R⁶ _(h)(R⁷O)_(i)SiO_((4-f-g-h-i)/2)  (VI) where R⁴ eachindependently are monovalent, SiC-bonded, optionally halogen- orcyano-substituted, hydrocarbyl moieties with aliphatic carbon-carbonmultiple bonding, R⁵ each independently are monovalent, SiC-bonded,optionally halogen- or cyano-substituted, saturated hydrocarbylmoieties, R⁶ each independently are monovalent SiC-bonded aromaticmoieties, R⁷ each independently are hydrogen or monovalent, optionallysubstituted hydrocarbyl moieties, which are optionally interrupted byheteroatoms, f is 0, 1, 2 or 3, g is 0, 1, 2 or 3, h is 0, 1 or 2, i is0 or 1, with the proviso that the f+g+h+i sum is not more than 3,siloxanes (B) have at least two R⁴ moieties per molecule, the f+g+h+isum is equal to 0 or 1 in not more than 20 mol % of the units of formula(VI) and h is other than 0 in at least one unit of formula (VI), (C) atleast one organopolysiloxane comprising units of the formulaR⁸ _(k)R⁹ _(l)R¹⁰ _(m)(R¹¹O)_(n)SiO_((4-k-l-m-n)/2)  (X), where R⁸ eachindependently are monovalent, SiC-bonded, optionally halogen- orcyano-substituted, hydrocarbyl moieties with aliphatic carbon-carbonmultiple bonding, R⁹ each independently are monovalent, SiC-bonded,optionally halogen- or cyano-substituted, saturated hydrocarbylmoieties, R¹⁰ each independently are monovalent SiC-bonded aromaticmoieties, R¹¹ each independently are hydrogen or monovalent, optionallysubstituted hydrocarbyl moieties, which are optionally interrupted byheteroatoms, k is 0, 1, 2 or 3, l is 0, 1, 2 or 3, m is 0, 1 or 2, and nis 0 or 1, with the proviso that the k+l+m+n sum is not more than 3,siloxanes (C) have at least two R⁸ moieties per molecule, the k+l+m+nsum is equal to 0 or 1 in at least 10 mol % of the units of formula (X)and m is other than 0 in at least one unit of formula (X), andoptionally, (D) a catalyst which promotes the addition of Si-bondedhydrogen onto aliphatic carbon-carbon multiple bonds.
 13. Thecomposition of claim 12, wherein siloxane(s) (A) comprise siloxaneshaving at least 3 units selected from the group consisting of theformulaeR¹ _(a)R² _(b)R³ _(c)H_(d)(RO)_(e)SiO_(1/2) where (a+b+c+d+e)=3  (II),R² _(b)R³ _(c)(RO)SiO_(2/2) where (b+c)=1  (IIIa),R² _(b)R³ _(c)SiO_(2/2) where (b+c)=2  (IIIb),R² _(b)R³ _(c)(RO)_(e)SiO_(3/2) where (b+c+e)=1  (IV), andSiO_(4/2)  (V), where R, R¹, R², R³, a, b, c, d and e are each asdefined above, with the proviso that not more than 25 mol % of the unitsin the siloxanes (A) are of formula (IIIb), the sum total of Si-bondedhydrogen atoms and R¹ moieties per molecule is at least 3, at least oneR³ moiety is present per molecule, and at least one unit of formula (IV)and/or (V) is present.
 14. The composition of claim 12, whereincomponent (C) comprises siloxanes consisting of units selected from thegroup consisting of:R⁸ _(k)R⁹ _(l)R¹⁰ _(m)(R¹¹O)_(n)SiO_(1/2) where (k+l+m+n)=3  (XI),R⁹ _(l)R¹⁰ _(m)(R¹¹O)SiO_(2/2) where (l+m)=1  (XIIa),R⁹ _(l)R¹⁰ _(m)SiO_(2/2) where (l+m)=2  (XIIb),R⁹ _(l)R¹⁰ _(m)(R¹¹O)_(n)SiO_(3/2) where (l+m+n)=1  (XIII), andSiO_(4/2)  (V) where R⁸, R⁹, R¹⁰, R¹¹, k, l, m and n are each as definedabove, with the proviso that siloxanes (C) have at least two R⁸ moietiesper molecule, at least one R¹⁰ moiety is present per molecule, and atleast one unit of formula (XIII) and/or (V) is present.
 15. Thecomposition of claim 13, wherein component (C) comprises siloxanesconsisting of units selected from the group consisting of:R⁸ _(k)R⁹ _(l)R¹⁰ _(m)(R¹¹O)_(n)SiO_(1/2) where (k+l+m+n)=3  (XI),R⁹ _(l)R¹⁰ _(m)(R¹¹O)SiO_(2/2) where (l+m)=1  (XIIa),R⁹ _(l)R¹⁰ _(m)SiO_(2/2) where (l+m)=2  (XIIb),R⁹ _(l)R¹⁰ _(m)(R¹¹O)_(n)SiO_(3/2) where (l+m+n)=1  (XIII), andSiO_(4/2)  (V) where R⁸, R⁹, R¹⁰, R¹¹, k, l, m and n are each as definedabove, with the proviso that siloxanes (C) have at least two R⁸ moietiesper molecule, at least one R¹⁰ moiety is present per molecule, and atleast one unit of formula (XIII) and/or (V) is present.
 16. Thecomposition of claim 12, comprising from 1 to 200 parts by weight ofsiloxane (C), based on 100 parts by weight of component (A).
 17. Thecomposition of claim 13, comprising from 1 to 200 parts by weight ofsiloxane (C), based on 100 parts by weight of component (A).
 18. Thecomposition of claim 14, comprising from 1 to 200 parts by weight ofsiloxane (C), based on 100 parts by weight of component (A).
 19. Thecomposition of claim 12, comprising: (A) siloxanes comprising units offormula (I), optionally (B) siloxanes comprising units of formula (VI),(C) siloxanes comprising units of formula (X), (D) a catalyst whichpromotes the addition of Si-bonded hydrogen onto aliphatic carbon-carbonmultiple bonds, optionally (E) fillers, optionally (F) adhesionpromoters, optionally (G) inhibitors, optionally (H) plasticizers,optionally (K) additives, and optionally (L) solvents.
 20. Thecomposition of claim 12, comprising: (A) siloxanes comprising units offormula (I), optionally (B) siloxanes comprising units of formula (VI),(C) siloxanes comprising units of formula (X), (D) a catalyst whichpromotes the addition of Si-bonded hydrogen onto aliphatic carbon-carbonmultiple bonds, optionally (E) fillers, (F) adhesion promoters,optionally (G) inhibitors, optionally (H) plasticizers, optionally (K)additives, and optionally (L) solvents.
 21. A process for producing acomposition of claim 12, comprising mixing the individual components inarbitrary order.
 22. A shaped article obtained by crosslinking acomposition of claim
 12. 23. The shaped article of claim 22, which is acoating, encapsulation, or lens.
 24. In a process for encapsulation ofelectrical or electronic components, the improvement comprisingencapsulating with a composition of claim
 12. 25. In a process for themanufacture of devices containing LEDs, the improvement comprisingencapsulating at least one LED with a composition of claim 12.